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56 TROP. LEPID. RES., 30(1): 56-57, 2020 HOULIHAN & SOURAKOV: Reflections on Morpho wings
Scientific Note: Capturing a green Morpho: In polarized low light in the
tropical rainforest, Morpho wing iridescence may contribute to camouflage
Peter R. Houlihan1,2,3 and Andrei Sourakov3
1
Department of Environmental Science & Policy, Johns Hopkins University; 2
Center for Tropical Research, Institute of the Environment & Sustainability,
UCLA; 3
McGuire Center for Lepidoptera and Biodiversity, Florida Museum of Natural History, University of Florida (location where research was conducted).
Date of issue online: 30 June 2020
Electronic copies (ISSN 2575-9256) in PDF format at: http://journals.fcla.edu/troplep; https://zenodo.org; archived by the Institutional
Repository at the University of Florida (IR@UF), http://ufdc.ufl.edu/ufir; DOI: 10.5281/zenodo.3899540
© The author(s). This is an open access article distributed under the Creative Commons license CC BY-NC 4.0 (https://creativecommons.org/
licenses/by-nc/4.0/).
Abstract: Morpho Fabricius, 1807 species have served as models for producing bioinspired materials with variable structural
colors, which have wide applications. Our recent field observation in French Guiana, suported by a lab experiment, demonstrates
that the dorsal surface of Morpho menelaus can produce cryptic green coloration in low-light reflected from green vegetation.
These observations are consistent with recently published evidence from experiments on jewel beetles that iridescent color is an
effective form of camouflage.
In the dark understory of the primary rainforest, a Morpho
menelaus (Linnaeus, 1758) (Nymphalidae) resting on vegetation
at 1.5 m above the ground was lightly contacted by our guide’s
machete to initiate a flight response (see Sourakov & Houlihan
(2017) for details about the study site). We fired two Canon
DSLR cameras simultaneously at the immediate moment when
the individual lifted off from the vegetation. One camera (an
older Ti) had an on-camera flash, while the other (a more recent
5Ds) had enough light sensitivity to freeze the specimen in
flight using ambient light only. Both cameras were operated in
manual mode. The colors in the two images contrasted greatly
(Fig. 1A,B): under natural light, the insect’s wings appeared
green, blending with the surrounding vegetation, the color of
which is accurately represented in the image (Fig. 1B). The
effect observed in the natural-light photo may have been due
to the prevalence of polarized green light in the environment,
since light coming from above was obscured by the dense
canopy. Using a museum specimen of M. menelaus, we took
photographs in the lab in varying light conditions (Fig. 1C,E).
An indirect white LED light shone through a green filter
and reflected from a green surface replicated almost exactly
the wing color of M. menelaus captured in situ in the forest
(Fig. 1D,E). One iconic aspect of Morpho Fabricius, 1807
butterflies is the presence in a number of species of colorless
scales covering large sections of their dorsal wing surfaces
(Ghiradella, 1991), which reflect visible light from different
angles and intensities in various shades color spectrum (Vukusic
et al., 1999; Vukusic & Sambles, 2003). The mechanism behind
this optical illusion is well-studied (Kinosh*ta et al., 2002), but
for detailed analysis of similarities and differences in optical
coloration of Morpho butterflies, one is referred to Berthier et
al. (2006), who clearly demonstrate (p. 150) the reflectivity
of M. menelaus scales and how it changes with light angle
and light mode. This latter study provides ample theoretical
explanations for our natural history observation presented
here. Another species with documented green reflectance in
a natural setting while flying in the canopy, Morpho rhetenor
(Cramer, 1775), was studied in detail by Plattner (2004), who
demonstrated that this species’ scales are adapted to reflect
most of the light below 550 nm at all angles with near-complete
transmission at wavelengths above the threshold of 550 nm.
As a result, this species’ wings could potentially serve as a
near-perfect mirror reflecting light coming from surrounding
vegetation. Interspecific differences in structural colors have
been linked not only to Morpho evolutionary history, but also
to the strata within the forest where species fly (Cassildé et al.,
2010). There has been an increasing number of applications
of these structural colors for engineering (e.g., Chung et al.,
2002), nanotechnology (e.g., Fu et al., 2016), and biomimicry
(e.g., Das et al., 2017). A new biosensor was developed by
culturing cardiomyocytes on M. menelaus’s wing surface, and
the contractions of these mammalian cells was detected through
optical color shifts from blue to green on the butterfly’s wings
(Chen et al., 2018). Beyond Morpho, two recent studies by
Kjernsmo et al. (2018, 2020) examined iridescence as a form
of camouflage, demonstrating that this optical phenomenon
may serve as a defensive trait through interference with object
recognition by predators. The role of iridescent coloration as a
predator-avoidance mechanism in Morpho butterflies remains
to be demonstrated experimentally.
ACKNOWLEDGMENTS
We thank the Florida Biodiversity Foundation for its
support of our fieldwork in French Guiana. We appreciate
the hospitality of Franck and Isabelle at Gite Moutouchi and
the kindness of their neighbor, George, on whose land the
observation was made, and whose guidance, keen eye, and
"The trees grew close together and were so leafy that he could get no glimpse of the sky. All the light was green light that came
through the leaves: but there must have been a very strong sun overhead, for this green daylight was bright and warm."
From The Magician's Nephew, by C. S. Lewis.
Nanomedicine and Nanobiotechnology 8(5): 758-775.
Ghiradella, H. 1991. Light and color on the wing: structural colors in butterflies
and moths. Applied Optics 30(24): 3492-3500.
Kinosh*ta, S., Yoshioka, S., Kawagoe, K. 2002. Mechanisms of structural
colour in the Morpho butterfly: cooperation of regularity and irregularity
in an iridescent scale. Proceedings of the Royal Society of London B:
Biological Sciences 269(1499): 1417-1421.
Kjernsmo, K., Hall, J. R., Doyle, C., Khuzayim, N., Cuthill, I. C., ScottSamuel, N. E., Whitney, H. M. 2018. Iridescence impairs object
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HOULIHAN & SOURAKOV: Reflections on Morpho wings TROP. LEPID. RES., 30(1): 56-57, 2020 57
machete were all instrumental in taking photos shared here.
We thank an anonymous reviewer for helpful comments which
improved this paper.
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Fig. 1. (A,B) Morpho m. menelaus, French Guiana, taking off. Two Canon DSLR cameras photos: (A) with built in flash (© Andrei
Sourakov); (B) with natural light (© Peter Houlihan). (C-E) Forewing of Morpho menelaus: (C) museum specimen illuminated by
incandescent light; (D) in situ, under low natural light of the forest understory, French Guiana (fragment of Fig. B); (E) museum
specimen illuminated by green light reflected from a green surface.
The journal Tropical Lepidoptera Research publishes original research on the systematics, biology and conservation of tropical and subtropical moths and butterflies.
